Oxidation resistant iron base alloy

ABSTRACT

Iron base alloys are disclosed containing certain alloying additions, which alloys exhibit unique and unexpectedly low weight gains when exposed to oxidizing environments. One of the major advantages of the alloys of the present invention lies in their moderate cost, especially as compared to other oxidation resistant iron base alloys, such as the various grades of stainless steel. The oxidation resistance of the alloys of the present invention is imparted through the formation of a tenacious, compact oxide film.

United States Patent [1 1 Caule et a1.

[111 3,811,874 [451' May 21, 1974 OXIDATION RESISTANT IRON-BASE ALLOY Inventors: Elmer J. Caule, NewHaven, Philip R. Sperry, North Haven; Michael]. Pryor, Woodbridge; James A. Ford,

North Haven, all of Conn;

Olin Corporation, New Haven, Conn.

Assignee:

Filed: Aug. 13, 1971 Appl. No; 171,432

Related US. Application Data Continuation-impart of Ser. Nos. 66,866, Aug. 25, 1970, Pat. No. 3,730,779, and-Ser. No. 750,99 Aug. 7, 1968,-abandoned.

U.s.ci..; ..7s/124 Int. Cl. C22c 39/54 Field of Search 75/124 1,128,726 2/1965 Rube] 75/124 2,835,570 5/1958 Klaybor 75/124 3,207,637 9/1965 Matuschka 75/124 422,403 3/1880 Hadfield 75/124 1,995,562 3/1935 Browne 75/124 2,140,237 12/1938 Leitneu 75/124 3,431,101 3/1969 Kunitake 75/124 Primary Examiner1-lyland Bizot Attorney, Agent, or Firm--Robert H. Bachman 57 ABSTRACT cost, especially as compared to other oxidation resistant iron base alloys, such as the various grades of stainless steel. The oxidation resistance of the alloys of the present invention is imparted through the formation of a tenacious, compact oxide film.

2 Claims, 4 Drawing Figures NUMBERS ATPO/NTS ARE WEIGHT GAINS IN MICRO- GRAMS PER CM PATENTEUHAY 2 x974 sum 10! 4 ALLOY2 ALLOY-l TEMPERATURE "c ATTORNEY PATEN'IEI] MY 2 1 i974 m i \Q tw I u ow N b: L..|| v m Q\ ELMERJ. CAULE PHIL/P R. SPERPY MICHAEL J. PRYOR JAMES A. FORD JNVENTORS ATTORNEY PATENTEDm 2 1 i974 SHEEIBUFQ TEMPERA TURE- "c N S 9 \wk $6 80$ iww INVENTORS. ELMER J. CAULE PHIL/P R. SPERRY MICHAEL J. PR 3mg AMES A. FORD ATTORN EY MENU-10mm I874 3 81 1 7 saw u or 4 A LLOY-J 2.000-

VVE/GHT GA/N M/CROGRAMS/ CM 2 ALLOY- 2 0 /00 200 300 460 500 ebo 760 860 TEMPERATURE c ELMER J. CA ULE PHIL/P R. SPERRY MICHAEL J. PRYOR JAMES A. FORD 4 v INVENTORS ATTORN EY 1 OXIDATION RESISTANT IRON BASE ALLOY CROSS REFERENCE TO RELATED APPLICATIONS This application is a continuation-in-part of copending application Ser. No. 66,866 now U.S. Pat. No.

3,730,779, May I, 1973 by Caule et al. for Oxidation Resistant Iron Base Alloy, filed Aug. 25, 1970, and copending application Ser. No. 750,99l now abandoned by Caule et al.'for Oxidation Resistant Iron Base Alloy, filed Aug. 7, 1968.

- BACKGROUND OF THE INVENTION It'has long been an objective of the art to provide low cost iron base alloys with oxidation resistance superior to that exhibited by the stainless steels. Presently,the

designed low alloy steels, such as Corten. One of the disadvantages of the mild steels'and specially designed lo'w alloy steels istheir extensive production of red r'ust rundown.

. shown in the instant specification, it has been found Accordingly, it is a principal object of the present invention to provide a low cost iron base alloy having oxidation resistance comparableto or superior to that exhibited by the stainless steels. I

It is a further object of the present'invention -to provide suchiron alloys which do not rely on large amounts of chromium in solid solution for their oxida- 1 red-rust rundown.

Further objectsand advantages of the present inven- I tion will appear from the ensuing specification.

SUMMARY OF THE INVENTION In accordance with the present invention it has been found that the foregoing objectsv and advantages may be readily achieved. v

The present inve-ntion-resides in an oxidation and tarnish resistant iron base alloy consisting essentially of that an iron-aluminum-silicon alloy of the present invention exhibits oxidation weight gain on the order of 50 times less than experienced by stainless steels or other iron base alloys. Further advantages and surprising characteristics of the alloys of the present invention will appear from the ensuing specification.

BRIEF DESCRIPTIONOF THE DRAWINGS num 2 percent silicon alloy containing 1.1 percent copper.

FIG. 2 is a ternary plot of iron-aluminum-silicon alloys of the present invention showing weight gains in micrograms persquare centimeterafter heating for 2 hours at 800C. FIG. 2 also shows for comparison the weight gains of binary iron-silicon alloys and binary iron-aluminum alloys. H

FIG. 3'is a graph showing oxidation weight gains at various temperatures for an iron-gallium-silicon alloy of the present invention.

FIG. 4 is a graph comparing the behavior of an iron-3 percent aluminum 2 percent silicon alloy of the present invention with type 301 stainless steel in a wet oxidizing, sulfur dioxide atmosphere.

The drawings will be discussed in more detail in the ensuing specification.

DETAILED DESCRIPTION As indicated hereinabove, the alloys of the present that which is achieved by stainless steels in the temper- (A) an alloyingadditionin an amount from I to7 percent byweight selected from'the group consisting'of beryllium,-aluminum, indiumand gallium and (B) .an

alloying additionin an amountfrom l to 4 percent by weight selected from the group consisting of silicon and germanium. g

The alloy of the present invention contains less than 0.25 percent copper. It has beenfound to be necessary to restrict the copper content in order to obtain the excellent oxidation resistance of thepresent invention.

'The alloyof the'pr'esent invention may contain phosphorus 0.04 percent max., sulfur 0.04 percent max.,

ature range from 300 to l,00OC.

The surprising oxidation resistance of the alloys of the present invention is achievedby the addition of specified alloying ingredients and by the-formation of a tenacious, compact substantially colorless-and adher-' ent oxide film.

The alloy of the present invention contains an alloying addition in the amount from-l to 7 percent selected from the group consisting of beryllium, aluminum, in-

diumand gallium.

Thealloy of the present invention also contains an alloying addition in the amount from I to 4 percent selected from the group consisting of silicon and germamum.

Representative specific combinations of materials are the following compositions: 3 percent beryllium 2' percent silicon; 3 percent indium 2 percent silicon; 3 percent gallium 2 percent silicon; 3 percent aluminum 2 percent germanium; and 3 percent aluminum 2 percent silicon.

The alloys of the present invention unexpectedly show a reversal in the plot of weight gain against temperature' as will be apparent from a consideration of the drawings which form a part of the present specification. This is believed to result from the formation of a tenacious, compact substantially colorless and adherent oxide film which contains iron plus one of the elements beryllium, aluminum, indium and gallium. For example, in the case where aluminum is used, there is formed aluminum oxide and a complex of the type Fe- 'Al O In the case where gallium is utilized, there is formed Ga O and a complex of the type FeO-Ga O The elements silicon and germanium are believed to stimulate the formation of oxides of this type.

In addition to the foregoing, it has been found that the copper content should be restricted to a maximum of 0.25 percent. It has been found to be necessary to restrict the copper content in order to obtain the excellent oxidation resistance of the present invention. In fact, it has been found that the higher copper contents yield poor oxidation resistance at both the lower and higher temperatures.

In addition to the foregoing, the alloys of the present invention may contain phosphorus 0.04 percent max., sulfur 0.04 percent max., manganese up to 1.5 percent and preferably up to 0.2 percent, others including nickel, molybdenum and vanadium and other alloying elements commonly present in low alloy steels may be present in an amount up to 0.20 percent. The carbon content may range as high as 2 percent for some applications requiring very high wear resistance. However, the carbon content is preferably not more than about 1 percent. Furthermore, the most preferred range of carbon is from 0.01 to 0.25 percent. It is expected that the latter range will have the most general application.

The iron base alloys of the present invention may be processed according to ordinary iron base alloy melting, casting, and hot and cold working procedures. It is an advantage of the present invention that the alloys of the present invention do not require specialized equipment or technology.

For example, the alloys of the present invention may be vacuum cast, homogenized, for example at l,800F, hot rolled to approximately 0.200", with a reheating to l,800F, if desired, scalped and cold rolled without interannealing to from 0.200" gage to 0.015" gage.

However, the alloy of the present invention does not require vacuum casting. Ordinary steel making procedures may be readily employed, as is well known in the art.

As indicated hereinabove, the alloys of the present invention are characterized by a great many highly desirable and in factsurprising characteristics. Particularly, the alloys of the present invention have surprising oxidation resistance, as has been discussed hereinabove. It is particularly significant that the alloys of the present invention achieve this surprising oxidation resistance while being considerably less expensive than alloys containing relatively large amounts of chromium, such as amounts of at least 5 percent and generally. above 11 percent. For example, the commonly used stainless steel which contains approximately 18 percent chromium and 8 percent nickel.

Furthermore, if one first forms the film of the present invention, subsequently the materials exhibit no further weight gain. This is particularly significant. Thus, for example, it has been found that the alloys of the present invention are highly resistant to atmospheric oxidation and tarnishing after first being exposed to a high temperature air oxidation of from 5 minutes to 100 hours at 400 to 1,000C and preferably 600 to 1,000C. Thus, 2 hours at 800C has been found to be very satisfactory.

The alloys of the present invention are characterized by the further advantage of excellent resistance to corrosion in ambient environments as compared to mild steel and specially designed low alloy steels, such as Corten. One of the disadvantages of the foregoing alloys is their extensive production of red rust rundown. On the other hand, the alloys of the present invention have shown as much as 50 to percent less'red rust rundown after one year of exposure.

It has also been found that the alloys of the present invention are highly resistant to contaminated atmospheres containing sulfur and/or water vapor and/or carbon monoxide-carbon dioxide combinations. These atmospheres are representative of most hydrocarbon combustion gases. The alloys of the present invention exhibit improved oxidation resistance in sulfur dioxide containing environments at elevated temperatures. in

addition, if the alloys of the present invention are pretreated in air at elevated temperatures, such as 800C in order to first form the film of the present invention, the instant alloys show substantial improvement over, for example, type 301 stainless steel over the entire temperature range, when treated in wet oxidizing, sulfur dioxide environments. Surprisingly, the weight gain shown by the alloys of the present invention is essentially zero at from above about 450C.

The present invention will be more readily understandable from a consideration of the following illustrative examples.

EXAMPLE I Iron base alloys were prepared by the following method. The alloys were cast by the vacuum melting technique. The castings were soaked at l,800F for 2 hours and hot rolled to 0.60" in four passes. The materials were reheated and soaked at l,800F for an additional 1% hours. Subsequently, the alloys were hot rolled to 0.20" in three passes. The hot rolled plates were scalped along both edges and top and bottom surfaces, leaving a finished gage of 0.17". The as-scalped plates were cold rolled to 0.015". All cold rolling was carried out without the benefit of further annealing.

EXAMPLE 11 After the procedure of Example I, the surface of the materials were cleaned and chemically polished. The specimens were oxidized for 2 hours in a horizontal tube furnace open at both ends to the atmosphere.

In this example, three alloy samples were studied having the composition indicated hereinbelow.

6 a weight gain substantially less than many types of stainless steels.

"l'ype l Stainless" Steel FIG. 1 shows the oxidation weight gain of Alloys 1, 2 and 3. It should be noted that Alloy 1, the alloy of the present invention exhibits a unique and unusual reversal in oxidation weight gain in the temperature range of 600 to 900C. This is in distinct contrast to the oxidation weight gain exhibited by stainless steel-type 301 (Alloy 2) over the same temperature range. Alloy 3 clearly shows that with higher copper'contents there results poor oxidation resistance at both the lower and higher temperature ranges.

Alloy l as characterized by having a tenacious, compact substantially colorless and adherent oxide film. Upon examination, this film was found to contain Al O anda complex of the type of FeO'Al- Om EXAMPLE III Example I II compares the weight gains in micrograms per square centimeter of various iron-aluminum-silicon alloys of the present invention after the alloys were heated for 2 hours at 800C. The materials were all prepared in a manner after Example I and treated in a manner after Example II.

The results are shown in FIG. 3 which is a ternary plot of the iron-aluminum-silicon alloys of the present invention. FIG. 2 also shows by comparison the weight gains of binary iron-silicon alloys and binary ironaluminum alloys.

It is apparent from a consideration of FIG. 2 that the alloys of the present inventionhave much lower weight gains than the binary alloys. In fact, from this data, it is apparent that weight gains below micrograms per square centimeter are assured for the 2 hour treatment at 800C.

EXAMPLE [V V EXAMPLE V In this example the behavior of Alloy 1 above in a wet oxidizing SO, atmosphere was compared with type 301 EXAMPLE Vl An alloy of the present invention. was prepared in a manner after Example I and processed as in Example II. The alloy had the following composition: aluminum- 3 percent, germanium-2 percent, copper-nil, iron essentially balance. The alloy exhibited the tenacious film of the present invention and showed improved oxidation resistance at 750C and above as compared to type 301 stainless steels.

This invention may be embodied in other forms or carried out in other ways without departing from the spirit or essential characteristics thereof. The present embodiment is therefore to be considered as in all respects illustrative and not restrictive, the scope of the invention being indicated by the appended claims, and all changes which come within the meaning and range of equivalency are intended to be embraced therein.

What is claimed is:

1. An oxidation and tarnish resistant iron base alloy consisting essentially of (A) an element in the amount from 1 to 7 percent selected from the group consisting of beryllium, aluminum, indium and gallium and (B) germanium in an amount of from I to 4 percent, said alloy having a copper content of less than 0.25 percent, phosphorus, 0.04 percent max., sulfur 0.04 percent max., manganese up to 0.2 percent, carbon up to l percent, balance iron, said alloy having a tenacious, compact, substantially colorless and adherent oxide film containing a complex oxide which contains iron plus one of said group (A) elements, said alloy having improved oxidation resistance and exhibiting a decrease in weight gain withincreasing temperature.

2. An iron base alloy according to claim 1 wherein said group (A) element is aluminum and said group (8). element is germanium. 

2. An iron base alloy according to claim 1 wherein said group (A) element is aluminum and said group (B) element is germanium. 